Mode-II fracture toughness and crack propagation of pultruded carbon Fiber-Epoxy composites

Abstract

This study develops a quasi-static mode II fracture toughness test methodology for pultruded carbon fiber-reinforced polymer (CFRP) composites along the fiber direction. The mode II fracture tests using a non-standard End-Notched Flexure (ENF) specimen as the pre-crack cannot be generated during the pultrusion process. A Compliance-Based Beam Method (CBBM) is used for data reduction, which does not require crack growth length monitoring during propagation and accounts for the effects of the Fracture Process Zone (FPZ) based on the equivalent crack growth length concept. When the test procedure is applied to the ENF specimens with different pre-crack sizes, the dependence of fracture behaviors on the pre-crack sizes is revealed according to the R-curves and crack growth rate curves. And the effects of the fracture process zone and damage accumulation development are revealed. Based on the analysis of fracture propagation behavior, the proper pre-crack size of the ENF specimen for testing the mode II fracture toughness of pultruded CFRP is determined, and fracture toughness of the investigated pultruded CFRP is obtained with the test results.